Electrical contact



Patented May 18, 1937 PATENT OFFICE f 2,080,811 nnnc'rrncar. CONTACT Kenneth L. Emmert, Indianapolis. Ind., assignmto P. It. Mallory & Co., Inc., Indianapolis, 1nd,. a corporation of Delaware No Drawing. Application, June 12, 1936, Serial No. 84,980

4 Claims.

This invention relates to electric contacts.

An object of the invention is to improve the characteristics of electric contact elements containing silver.

6 Other objects of the invention will be apparent from the following description taken in connection with the appended claims.

The present invention comprises the combination of elements, methods of manufacture, and the product thereof brought out and exemplified in the disclosure hereinafter set forth, the scope of the invention being indicated in the appended claims.

While a preferred embodiment of the invention 15 is described herein, it is contemplated that considerable variation may be made in the method of procedure and the combination of elements with-,

out departing from the spirit of the invention.

The present invention comprises an improvement in silver electric contact elements and especially in contact elements formed of silver and cadmium. According to the invention the contacts are improved by the addition of nickel.

The contacts accordingly may be composed of 25 cadmium nickel and silver. The ingredients may be present in approximately the following proportions:

Per cent Nickel 1 0.25 to 30 Cadnn A 5 to 25 Silver balance A preferred contact material has the composition:

for use as make-and-break contacts for controlling either A. C. or D. C. circuits. They may be used in pairs of the same composition or an individual contact of this composition may be used with a co-operating contact -of entirely difierent composition.

The addition of nickel as set forth above materially improves the contact characteristics. It also increases the resistance of the contact material to cold working and thereby maintains contact spacing. The nickel increases the fusing temperature of the contacts thus greatly reducing the possibility of the contacts melting and sticking together during heavy current surges.

60 The cadmium reduces the tendency toward metal transfer and build-up and reduces the tendency of the contacts to fuse together.

The contacts of the present invention are particularly satisfactory for use on low frequency relays and on contact applications where the contacts are subject to momentary overload where prior contact materials cause undue failure by fusion and sticking.

Comparative tests have been made on contacts of the first preferred composition given above and contacts of fine silver. coin silver and an alloy of 80% silver plus 20% cadmium.

The various contact materials were tested on Cutler-Hammer relays using one pair of contacts 0.187 diameter one of which was flat faced and the other having approximately a 1" radi'us. The contacts were riveted on phosphor bronze reeds with .the maximum opening about 6 volts D. C. 1.5 amperes 12 volts D. C. 2.1 amperes 110 volts D. C.- 1.8 amperes 18 .volts A. C.-- 6.7 amperes 110 volts A. C.-- 6.7 amperes 220 volts A. C.10.0 amperes The principal results discussed below show the superiority of the contacts of the present invention:

Sticking or failure due to arcing During a test period of 72 hours operation at 110 volts D. C. failure occurred before the end of the period on all the comparison materials whereas the contacts of the present invention were still operating at the 'end of the test period as indicated in the table below:

- Material Lg Number of operations Metal transfer and pitting Fine silver showed the greatest tendency toward pitting and transfer, followed in order by the 80-20 alloy and the alloy of the present regard.

Oxidation The alloy of the present invention showed slightly less oxidation than the 80-20 alloy,

transfer. Therefore the comparison-materials.

showed a tendency toward greater wear than the alloy of the present invention.

Contact resistance ation is in general an indication of the operating characteristics of the contact material. An increasing contact resistance with length .of oper- 0 ation indicates the formation of a high resistance oxide or a pitting or wearing of the contact face.

Increased resistance causes an increased tendency toward overheating and contact sticking.

The initial resistance of contacts made of the 5 alloy of the present invention was lower than that r P of the 8020 alloy and of coin silver. Fine silver generally has a lower initial resistance than all the others and remains constant on low current operation. However, its contact resistance in- 0 creases very greatly with heavy loads frequently resulting in sticking.

The 80- alloy showed a greater increase in resistance during operation than any. others.

The change in contact resistance during oper- 2,080,811 invention. Coin silver was not compared in this Coin silver showed a decrease. The alloy of the present invention was generally more constant with all current loads and with light-and heavy contact pressures. 2 Contacts made of materials containing normal amounts of impurities are contemplated as within the scope of the present invention. 1

While the present invention as to its objects and advantages, has been described herein as carried out in specific embodiments thereof, it is not desired to belimited thereby but it is intended to cover the invention broadly within the spirit'and scope of the appended claims.

What is claimed is:

1. An electric contact member consisting of an alloy of 5 to cadmium, 0.25 to 5% nickel and the balance silver.

2. An electric contact member comprising an alloy of about 22.4% cadmium, about 0.6% nicke and the balance silver.

3. An electric contact member comprising an alloy of about 20% cadmium, about 2% nickel and the balance silver.

4. An electric contact member comprisingan alloy consisting substantially of cadmium, nickel and silver, the cadmium comprising substantially 5 to 25% of said alloy, the nickel comprising ,substantially 0.25 to 5% of said alloy and the remainder of said alloy ,conslsting substantially of silver. J L. "EMMERT. 

